The present invention relates to a method to estimate a transmission channel characteristic, a transmission channel characteristic estimating arrangement able to perform this method, and a related remote terminal.
Such a method to estimate a transmission channel characteristic and related equipment are already known in the art, e.g. from the U.S. Pat. No. 4,105,995, entitled xe2x80x98Digitally Controlled Transmission Impairment Measurement Apparatusxe2x80x99. Typically, the operator needs knowledge of certain channel characteristics of a transmission channel between a central office and a remote terminal to be able to guarantee a certain service to a subscriber that has installed the remote terminal. The presence of line imperfections such as bridged taps, line attenuation, ageing effects, disturbers like radio frequency interference, and so on, has to be estimated by the operator before a certain quality of service can be guaranteed. To estimate all basic parameters necessary to characterise a transmission channel for its ability to carry data traffic, U.S. Pat. No. 4,105,995 describes a portable microprocessor controlled apparatus that measures specified parameters for a telephone channel. The known apparatus for channel characteristic estimation either consists of two units to be connected respectively to both ends of the transmission channel, or of a single unit to be connected to a single end of the transmission channel. The latter embodiment of the known channel characteristic estimating apparatus requires manual loop-back at the end of the transmission channel whereto the apparatus is not coupled. Summarising, U.S. Pat. No. 4,105,995 describes dedicated transmission channel test equipment enabling off-line measurement of channel characteristics. To apply the known technique, transmission of user data over the transmission channel has to be interrupted and test equipment has to be connected to the transmission channel either at one or at both sides of the channel.
It is an object of the present invention to provide a method for estimation of a transmission channel characteristic and related equipment similar to the above described one, but which allows both on-line and off-line channel characteristic estimation without the necessity to connect dedicated test equipment to the transmission channel.
According to the invention, this object is achieved by the method to estimate a transmission channel characteristic, the transmission channel characteristic estimating arrangement, and the remote terminal.
Indeed, the remote terminal itself collects all information required to estimate the transmission channel characteristic of interest and sends this information back to the central office wherein the information is matched with a simulation model of the transmission channel and remote terminal. The information collected by the remote terminal can be fed back in a multiplexed way simultaneously with user data so that the data traffic over the transmission channel does not have to be interrupted. The simulation model used in the central office for the matching process typically contains a number of parameters, e.g. the location along the transmission line of a bridged tap, corresponding to the transmission channel characteristics of interest. During the matching process, the values of these parameters are determined.
It is to be noticed that the term xe2x80x98comprisingxe2x80x99, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression xe2x80x98a device comprising means A and Bxe2x80x99 should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noticed that the term xe2x80x98coupledxe2x80x99, also used in the claims, should not be interpreted as being limitative to direct connections only. Thus, the scope of the expression xe2x80x98a device A coupled to a device Bxe2x80x99 should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.
Indeed, the remote terminal of an Asymmetric Digital Subscriber Line (ADSL) system operating in accordance with ANSI""s T1.413 standard, issue 2 for instance automatically collects information concerning the attenuation of a set of carriers with equidistant frequencies as can be deduced from paragraph 9.9.8.1 of the draft edition of issue 2 of ANSI""s T1E1.413 standard, entitled xe2x80x98Standards Project for Interfaces Relating to Carrier to Customer Connection of Asymmetric Digital Subscriber Line (ADSL) Equipment. This information is collected for use in the bit rate selection process described in paragraph 9.9.8.2 of the cited draft standard, and for use in the bit allocation process described in paragraph 9.9.14 of the cited draft standard, but in addition is very useful for estimating certain transmission channel characteristics such as the position of a bridged tap along the line. A preferred embodiment of the present invention consequently makes use of this automatically collected information for transmission channel characterisation.
Thus, by multiplexing the collected information that will be used for transmission channel characterisation with user data, a transmission channel can be characterised without interruption of the system. This is so because the remote terminal that is able to transmit the user data does not have to be replaced by test equipment.
Alternatively, a transmission channel characteristic is estimated off-line.
Thus, by interrupting transfer of user data over the channel and bringing the system into a test phase, a transmission channel characteristic according to the present invention can also be estimated off-line without the requirement to connect dedicated test equipment to the channel.
In this way, information indicative for the attenuation and phase rotation of carriers having different frequencies, such as is typically collected in a multi-carrier ADSL (Asymmetric Digital Subscriber Line) modem and used therein for setting equaliser coefficients, can additionally be used for channel characterisation.
In this way, information indicative for the noise affecting carriers having different frequencies, such as is typically collected in a multi-carrier ADSL modem and used therein for allocation of bits to carriers, can additionally be used for channel characterisation.
Furthermore, the present invention is very suitable for implementation in an Asymmetric Digital Subscriber Line (ADSL) system, or any similar system, e.g. a Very High Speed Digital Subscriber Line (VDSL) system.
An additional advantageous feature of the arrangement for estimating a transmission channel characteristic.
Hence, information suitable for use in the transmission channel characterisation method can be collected over a certain time interval, and can be fed back to the central office as soon as this time interval has elapsed.